Crosslinking agent for a crosslinkable silicone composition with a low level of platinum based on a hydrogenated silicone oil comprising Si-H units at the chain end and in the chain

Abstract

The invention concerns crosslinkable silicone compositions, useful for forming water-repellent and release coating for flexible heat-sensitive support. Said compositions comprise crosslinking polyorganosiloxanes (POS) bearing ≡Si—H units and unsaturated POS, for example ≡Si-Vi vinyl-containing POS, capable of reacting with the crosslinking agent by polyaddition, in the presence of platinum to form a release crosslinked coat on the flexible support. The invention aims at instantaneously enabling low platinum content crosslinking of such silicone compositions, coated at high speed. Therefor, the invention provides for the use of particular crosslinking agents consisting of hydrogenated POS comprising at least three hydrogen atoms bound to the silicon located at chain end and in the chain. The invention also concerns solvent-free or emulsion-type silicone compositions comprising the ≡Si-Vi POS (I.1), the crosslinking agent ≡Sl-H POS (l.2) and the platinum catalyst among others. The invention is useful for coating flexible supports, for example made of Lissé BEKK>1000 paper.

1. A crosslinking agent (I.2), for use in a silicone composition capable of crosslinking by polyaddition in the presence of a metal catalyst to form a water-repellent and release coating for a fibrous or nonfibrous support,
 of at least one silicone oil comprising at least one hydrogenated (optionally linear) PolyOrganoSiloxane (POS) exhibiting, per molecule, at least three hydrogen atoms bonded to silicon atoms, and having the following mean formula:
   M α M′ β D γ D′ δ   
 
 with M=(R 1 ) 3 SiO 1/2  
 M′=H a (R 1 ) b SiO 1/2 , a+b=3, a=1, 2 or 3, 
 b=0 to 3 
 D=(R 2 ) 2 SiO 2/2    
 D′=HR 3 SiO 2/2    
 0≦α≦2 
 0<β≦2 
 0<γ 
 0<δ 
 
 and with:
 0<γ/δ≦0.4, 
 20≦(β/δ)×1000≦60, and wherein R 1 ,R 2  and R 3  are alkyl groups having from 1 to 8 carbon atoms, 
 
 the POS having a dynamic viscosity η at 25° C. of less than or equal to 1500 mPa·s. 
 
     
     
       2. A silicone composition comprising a crosslinking agent capable of crosslinking by polyaddition in the presence of a metal catalyst to form a water-repellent and release coating for a fibrous or nonfibrous support,
 of at least one silicone oil comprising at least one hydrogenated (optionally linear) PolyOrganoSiloxane (POS) exhibiting, per molecule, at least three hydrogen atoms bonded to silicon atoms, and having the following mean formula:
   M α M′ β D γ D′ δ   
 
 with M=(R 1 ) 3 SiO 1/2  
 M′=H a (R 1 ) b SiO 1/2 , a+b=3, a=1, 2 or 3, 
 b=0 to 3 
 D=(R 2 ) 3 SiO 2/2    
 D′=HR 3 SiO 2/2    
 0≦α≦2 
 0≦β≦2 
 0<γ 
 0<δ 
 
 and with:
 0<γ/δ≦0.4, 
 20≦(β/δ)×1000≦60, and wherein R 1 ,R 2  and R 3  are alkyl groups having from 1 to 8 carbon atoms, 
 
 the POS having a dynamic viscosity ηat 25° C. of less than or equal to 1500 mPa·s; 
 the level of metal catalyst being less than or equal to 80 ppm, wherein the silicone composition is such that it can be converted to a croddlinked silicone elastomer coating on a support made of paper with a Bekk smoothness of greater than 1,000, said coating having a postive attachment in a specific test T. 
 
     
     
       3. A coated support comprising a coating comprised of a silicone composition comprising a crosslinking agent capable of crosslinking by polyaddition in the presence of a metal catalyst to form a water-repellent and release coating for a fibrous or nonfibrous support; the crosslinking agent comprising
 at least one silicone oil comprising at least one hydrogenated (optionally linear) PolyOrganoSiloxane (POS) exhibiting, per molecule, at least three hydrogen atoms bonded to silicon atoms, and having the following mean formula:
   M α M′ β D γ D′ δ   
 
 with M=(R=(R 1 ) 3 SiO 1/2  
 M′=H a (R 1 ) b SiO 1/2 , a+b=3, a=1, 2 or 3, 
 b=0 to 3 
 D=(R 2 ) 2 SiO 2/2    
 D′=HR 3 SiO 2/2    
 0≦α≦2 
 0≦β≦2 
 0<γ 
 0<δ 
 
 and with:
 0<γ/δ≦0.4, 
 20≦(β/δ)×1000≦60, and wherein R 1 , R 2  and R3 are alkyl groups having from 1 to 8 carbon atoms, 
 
 the POS having a dynamic viscosity η at 25° C. of less than or equal to 1500 mPa·s; 
 the level of metal catalyst being less than or equal to 80 ppm, wherein the silicone composition is such that it can be converted to a crosslinked silicone elastomer coating on a heat-sensitive material, optionally selected from flexible supports made of paper, board, flexible supports composed of the adhesive face of a label or of a tape of the same kind, woven or nonwoven fibrous flexible supports, flexible supports comprising polyethylene and/or polypropylene and/or polyester and/or poly(vinyl chloride), and/or thermally printable flexible supports. 
 
     
     
       4. The support as claimed in  claim 3 , wherein, for the crosslinking of the coating, the support is placed at a temperature of less than or equal to 110° C., for less than 60 seconds. 
     
     
       5. The composition agent as claimed in  claim 2 , wherein the composition is a mixture formed of:
 (I.1) at least one ≡Si-alkenyl POS exhibiting, per molecule, at least two alkenyl groups bonded to silicon atoms, 
 (1.2) at least one crosslinking ≡Si—H POS as defined above, 
 (1.3) and/or at least one POS carrying Si-alkenyl and Si—H units, 
 (II) at least one catalyst (II) comprising at least one metal belonging to the platinum group. 
 
     
     
       6. The composition as claimed in  claim 5 , wherein the crosslinking POS exhibits an ≡Si—H/≡Si-alkenyl (Vi) molar ratio such that:
   1.0≦≡Si—H/≡Si-alkenyl(Vi)≦4. 
 
     
     
       7. The composition as claimed in  claim 6 , wherein the POS (I.1) is a product comprising units of formula: 
       
         
           
             
               
                 
                   
                     
                       W 
                       a 
                     
                     ⁢ 
                     
                       Z 
                       b 
                     
                     ⁢ 
                     
                       SiO 
                       
                         
                           4 
                           - 
                           
                             ( 
                             
                               a 
                               + 
                               b 
                             
                             ) 
                           
                         
                         2 
                       
                     
                   
                 
                 
                   
                     ( 
                     
                       I 
                       ⁢ 
                       .1 
                     
                     ) 
                   
                 
               
             
           
         
       
       in which:
 W is an alkenyl group, 
 Z is a monovalent hydrocarbonaceous group which has no unfavorable effect on the activity of the catalyst and which is selected from alkyl groups having from 1 to 8 carbon atoms inclusive, optionally from the methyl, ethyl, propyl and 3,3,3-trifluoropropyl groups, and also from aryl groups, optionally from the xylyl, tolyl and phenyl radicals, 
 a is 1 or 2, b is 0, 1 or 2 and a+b is between 1 and 3. 
 
     
     
       8. The composition as claimed in  claim 2 , wherein the release crosslinkable silicone composition futher comprises:
 at least one adhesion-adjusting system (III), 
 and/or at least one agent for inhibiting hydrosilylation (IV). 
 
     
     
       9. The crosslinking agent as claimed in  claim 5 , wherein the POS (I.1) is a blocked linear polydiorganosiloxane comprising “Si-alkenyl” functional groups, exhibiting a viscosity of the order of 100 to 1000 mPa·s and a level of alkenyl functional groups I a , expressed as equivalent number of alkenyl functional groups per 100 g of oil, of:
 0.010≦1 a . 
 
     
     
       10. The composition as claimed in  claim 5 , wherein at least one POS comprising ≡Si—H functional groups (I.2) exhibits a viscosity of the order of 5 to 150 mPa·s. 
     
     
       11. The composition as claimed in  claim 2 , wherein the composition is provided in the form of an aqueous emulsion/dispersion. 
     
     
       12. A silicone composition capable of crosslinking by polyaddition to form a water-repellent and release coating for a fibrous or nonfibrous support,wherein the composition comprises:
 (I.1) at least one POS exhibiting, per molecule, at least two alkenyl groups bonded to silicon atoms, 
 (I.2) at least one silicone oil:
 comprising at least one hydrogenated linear PolyOrganoSiloxane (POS) exhibiting, per molecule, at least three hydrogen atoms bonded to silicon atoms, 
 and having the following mean linear formula:
   M α M′ β D γ D′ δ   
 
 
 with M=(R 1 ) 3 SiO 1/2  
 M′=H a (R 1 ) b SiO 1/2 , a+b=3, a=1, 2 or 3, b=0 to 3 
 D=(R 2 ) 2 SiO 2/2    
 D′=HR 3 SiO 2/2    
 0≦α≦2 
 0<β≦2 
 0<γ 
 0<δ 
 
 and with:
 0<γ/δ≦0.4, 
 20≦(β/δ)×1000≦60, and wherein R 1 , R 2  and R3are alkyl groups having from 1 to 8 carbon atoms, 
 
 at least one catalyst (II) comprising at least one metal belonging to the platinum group; said catalyst being present at a level of metal catalyst being of less than or equal to 80 ppm; 
 and in that the POS has a dynamic viscosity 1η at 25° C. of less than or equal to 1500 mPa·s. 
 
     
     
       13. A composition prepared using the crosslinking agent as claimed in  claim 1 . 
     
     
       14. A support comprising at least one release coating obtained
 crosslinking the coating composition with the crosslinking agent as claimed in  claim 1 .